The invention relates to a flat accumulator device including a planar electrochemical cell with at least two planar electrodes having opposite polarities disposed on either one of the two sides of an electrolyte material, a planar housing having planar parts and enveloping said planar electrochemical cell, and electrical contact means of the electrodes forming external electric terminals fixed in a moisture-proof manner to the planar parts of the housing.
The invention finds its application in the manufacturing of electric batteries or for rechargeable batteries applied to portable apparatus such as telephone terminals.
A device of the flat and thin accumulator type having an electrochemical cell, a housing and contact means forming external terminals is already known from Japanese patent JP-62-216151 (Matsushita Electric Ind. Co. Ltd. Minoru Yoshinaka). The known housing comprises two plane walls i.e. a lower wall and an upper wall made of a non-conductive material (polycarbonate resin) separated by a plastic body enveloping an electrochemical cell. This electrochemical cell comprises lead electrodes applied against the plane lower and upper walls of the housing. A security valve, disposed through the body of the housing permits of diminishing an occasional internal overpressure of this electrochemical lead cell. The plane upper and lower walls comprise each a current collector in the form of a flat copper plug, passing through said wall to ensure an electrical contact between the electrodes and the exterior of the housing. One point is that the impermeability of these plugs is realized by heating and melting the plane walls, the plugs and the electrodes together to ensure a cohesion of these parts. Another point is that the electrodes are, in addition, made integral with the body of the housing by heating. The plugs are used as positive and negative external contacts of the housing. These plugs have no protrusions so that the housing of the accumulator is thin and flat.
A technical problem is linked with the electrochemical cells called rechargeable chemical batteries. To ensure their operation, certain batteries such as the lead-acid batteries are from the start under a pressure that exceeds the atmospheric pressure. In the case of such batteries, an occasional overpressure may occur during the recharging operation. Other rechargeable chemical batteries, although they do not work in a state of overpressure, may none the less occasionally be subjected to a phenomenon of overpressure. Such a phenomenon may occur, for example, as a result of the fact that during the recharging operation a connection of the battery is defective. The defective connection may be the cause of a short-circuit which generates a rapid release of gas due to an unwanted chemical reaction between the various elements of the cell, and which results in an overpressure in the housing accompanied by a rapid rise of temperature. This reaction may then result in an explosion due to the overpressure, with a fusion of the materials due to the risen temperature.
In the known device, the problem of overpressure is taken into account and resolved by an air hole in the form of a pipe through the body of the housing. This air hole permits of the ejection of a small plug placed on the outer end of the pipe for diminishing the pressure inside the housing and avoiding the explosion of the device.
Another technical problem is that inside an electrochemical cell it is impossible to have an assembly of metallic parts of different metals, soldered or mating and enveloped in the electrolyte. This type of assembly is absolutely to be outside the chemical environment formed by the electrolyte.
In the known device, this problem is taken into consideration and solved by the fact that the lead electrodes are soldered on the whole internal surface of the plane walls of the housing and are soldered furthermore along their periphery between the body and the plane walls of the housing, so that the lead-copper soldering of these electrodes with the plugs which are used as external contacts is not enveloped in the electrolyte.